Thanks Woody, I don't think Dad had the extended warrantee. I inherited the buick a few years ago and did not add warrantee coverage.

You don't have to buy an extended warranty. The warranty coverage by GM has been extended on this particular part. It's called a "special policy" and covers every vehicle listed, as long as it hasn't been totaled.

I had an 08 Enclave AWD and had to drop the cradle to fix. Not too bad of a job if you have a lift.
changed the wave plate, and found it was not broken. The TCM was the problem, it is a large overmolded plastic assembly with the pressure and temp sensors in it. I bought a new assembly from the dealer for about $700. Installed it, reflashed, and it was then perfect.

I never had the trans temp warning come on...the temps were fine. fluid was clean... I kept getting codes saying the line1-2 pressure was low or something like that and it would not shift out of first gear.
Upon examination, the overmolded TCM assembly from Borg Warner was coming apart. The pressure sensors have some sort of encapsulant that was dislodged and floating around in the fluid.
I think the thermistor is in that same TCM assembly...so if the fluid is clean and the wave plate is not broken...it is likely the TCM needs replaced.
Dealers will have them, maybe in stock. You will need to reprogram the TCM before driving the vehicle, in my case I had a friend that works at GM dealer stop over and do it, handed him $50.

I really liked the Enclave and the wife did too. Just didn't like the maintenance needed...when I dropped the cradle, I went ahead and replaced all that typically goes wrong with them.
replaced the timing chains and tensioners
replaced steering rack
new plugs
new cam position sensors
new water pump

after I did all that it ran like a top.

Woody b's advice is spot on, if the wave plate is in fact the issue, they should cover it. In my case I was pretty sure it was not the wave plate, since it didn't show the same symptoms of the broken plate. My suspicion was right, cause the plate was fine once I got in there. i replaced it anyway with the new p/n that is supposed to be better.
If the dealer tears into it, and it is not the plate being the root cause....you will get hit with the large bill

Dropped off at Buick this morning, last thing I had serviced at a dealer was when I broke my 14 bolt Swiss watch rear in the old work truck back in '88. I expect to be abused hard. The wife said I am paranoid. Thanks, Charlie

Wiffy said the service engine soon light came on while bringing the car in today. The tech funny as it may be could not find any history of a tranny overtemp or codes. He thinks it is the tranny temp sensor. I told him about my friend who rebuilt many of those trannies and I think the 35r waveplate started to go and the debris plugged the cooler. The tech will take it home tonight with the scanner on. Woody, thanks for the help!

It will resurface.....if it is the TCM assembly...will eventually fail.
if it's debris clogging the cooler....it may come and go randomly

on mine, it popped code...wouldn't shift out of first.
First time, I told the wife just pull over, and turn the car off, and back on. She did and it then shifted thru gears and ran ok.

I would clear the codes that night, with HP tuners....and then wife would drive it sometimes for weeks until it came back.

After it happened 2 or 3 times...I dropped the cradle and prepared to weigh my options on a rebuilt trans.
When I took it apart, the fluid was clean and not dark. The wave plate was not broken...so I started to look at other areas and found the TCM coming apart. Dealer had one in stock, which to me says this is a fairly common occurrence.

Dealership diagnosis fail. (I'm not surprised.) I'd be tempted to obtain an OBDII scanner that allows you to display live data (there are plenty of them out there) and drive around monitoring trans temperature so that you can see what the computer is seeing, and perhaps identify pipes/hoses in the engine compartment that pertain to the transmission cooler and check if what the computer is seeing is plausible reality (i.e. is the transmission really running that hot? is the flow to/from the cooler actually happening?)

Do check the fluid level; it appears that this transmission model is sensitive to it with running hot being a consequence of being overfilled.

Not sure if you've got this fixed yet. If you want to find out if it's a broken wave plate, get a cake pan and take a sample of fluid out of the trans drain plug. don't have to drain the whole thing, just a little bit into the pan. Then have a look. If there is excessive metallic, 95% chance it's a broken wave plate. I own a transmission shop and have never seen this trans failed in a Ford---yet. If you're wondering, GM 6T75 and Ford 6F50----same thing, designed as joint venture between GM and Ford. Everytime GM 6T75 comes in, it has or had a broken wave plate. Difference was Ford shotpeened the wave plates, GM did not. GM does now.
If the dealer just scanned for codes and did not take a fluid sample, then it wasn't a thorough diagnostic. If you can pull a drain plug, find out first hand.

Not sure if you've got this fixed yet. If you want to find out if it's a broken wave plate, get a cake pan and take a sample of fluid out of the trans drain plug. don't have to drain the whole thing, just a little bit into the pan. Then have a look. If there is excessive metallic, 95% chance it's a broken wave plate. I own a transmission shop and have never seen this trans failed in a Ford---yet. If you're wondering, GM 6T75 and Ford 6F50----same thing, designed as joint venture between GM and Ford. Everytime GM 6T75 comes in, it has or had a broken wave plate. Difference was Ford shotpeened the wave plates, GM did not. GM does now.
If the dealer just scanned for codes and did not take a fluid sample, then it wasn't a thorough diagnostic. If you can pull a drain plug, find out first hand.

Ok, Sunday job. Sample of tranny fluid. Black and stinks. Looks much different than on dipstick. Not sure what they use for diff fluid on awd but it is tranny fluid. There are flakes of metal on bottom of glass. I could use some input by tranny experts on what I should do next. Just do a fluid change and filter or bring it back to GM for them to tell me tranny is fine. It has not overheated again but has not been driven over an hour either! Thanks, Charlie